In paper manufacture, a fibre slurry is firstly produced, which is an aqueous suspension comprising starting materials such as fibrous constituents and possibly further papermaking auxiliary agents. This papermaking stock is passed in web form onto a belt-type screen containing drainage elements. After partial drainage the web passes through a so-called sizing press, in which starch is applied as sizing agent to the partially dried web in the form of an aqueous suspension to increase the tear resistance of the paper to be manufactured.
Since the starch in question is a processed product, which is relatively expensive to produce and is thus associated with corresponding costs, it was desirable to replace the starch with a cheaper raw material.
Thus, it is proposed in DE 43 44 139 A1 to substitute cereal flour such as rye flour, for example, for the starch, wherein the cereal flour is extruded to homogenise it and is then ground to a powdered product. Extrusion serves to prevent lump formation during the necessary dispersion of the cereal flour for use in paper manufacture.
To assure an undisturbed operation for the paper manufacture and additionally constant quality of the paper obtained, it is necessary that an even homogeneous application of the aqueous suspension serving as sizing agent is assured over longer periods of operation. Moreover, no sedimentation should occur in the suspension.
Therefore, an aqueous suspension of cereal flour, such as that to be used as sizing agent in paper manufacture, for example, should have a high suspension stability, wherein there should also be no substantial change in viscosity over a longer period of time and moreover no, or substantially no, sedimentation should occur.
DE 197 29 272 relates to starch-based thermoplastic mixtures, wherein starch is modified with a phosphate, amongst others sodium trimetaphosphate, and the components are mixed by application of thermal and mechanical energy preferably at elevated temperature and with simultaneous exertion of shearing forces. The mixing can be conducted in conventional single- and double-screw extruders.
The aim was to obtain starch-based moulding materials, which exhibit a thermoplastic behaviour enabling them to be processed by means of known plastic processing techniques to form mouldings with adequate mechanical properties such as, for example, an adequate strength and a sufficient dimensional stability.
Moreover, it is stated that the obtained products can be used, inter alia, as adhesives for paper and corrugated cardboard. Adhesives are used to glue individual paper layers, as is necessary, for example, in the manufacture of corrugated cardboard from several paper layers.
However, no further details are given regarding the suitability for paper manufacture, in particular for sizing.